The present invention is an improvement on the copending application of Robert B. Enemark, entitled Battery Powered Smoke Detector, Ser. No. 718,686, filed Aug. 30, 1976, now abandoned and continued in application Ser. No. 872,674, which is incorporated herein by reference. The operation of the detector of that copending application which senses reduced or declining battery voltage only is to be distinguished from the object of the present invention which is to discriminate against batteries whose voltage may be adequate but which are unable to deliver sufficient energy to the smoke detector circuits particularly the detector alarm.